Multi-layer film cut filter and production method therefor, UV cut filter, dustproof glass, display panel and projection type display unit

ABSTRACT

A multi-layer film, wherein a ratio H/L or L/H, a balance in optical film thickness between a high-refractive-index layer H and a low-refractive-index layer L, is set within a range of 1.2–2.0 to bias a balance in thickness. A method of producing a dielectric multi-layer film, wherein, when a dielectric multi-layer film is formed, a proportion at which an optical film thickness is formed on a monitor substrate is made larger than usual. A UV reflection film, having a step difference in average transmittance of 70–90% at a specified half-power point and within a wavelength range of 430–450 nm, is provided on a substrate to form a UV cut filter. A UV reflection film at a specified half-power point, a step difference in average transmittance of 70–90% within a wavelength range of 430–450 nm, and a blue conditioning film having a transmittance of at least 90% within a wavelength range of 460–520 nm may be combined. This UV cut filter is applied to the projection type display unit of a ultra-high pressure mercury lamp light source. The UV reflection film may be provided on the dustproof glass of a display unit.

TECHNICAL FIELD

The present invention relates to an optical filter technology forcutting light of wavelengths shorter than a specified wavelength andtransmitting light of longer wavelength and a production methodtherefor, a dustproof glass utilizing the optical filter technology, adisplay panel for image formation which is used in a projection typedisplay unit using the dustproof glass, and a projection type displayunit such as a liquid crystal projector using the display panel.

BACKGROUND ART

As to a liquid crystal projector for enlarged projection of images, anincrease in luminance and a decrease in size have been progressing yearby year, and a high-output ultra-high pressure mercury lamp generatingstrong UV rays has come to be used as a light source. Since the opticalsystem has been reduced in size, the energy density of the lighttransmitted through the optical system has been enhanced. Therefore, theproblem that the component parts using an organic material such as aliquid crystal panel, a polarizing plate, a phase difference plate, etc.which are used in the optical system inside the liquid crystal projectorare deteriorated principally by the UV rays and further byshorter-wavelength rays among visible rays with the result of areduction in display quality in a short time has become greater. Inaddition, there is the problem that the liquid crystal display panelabsorbs such light to be raised in temperature through heat generation,leading to generation of non-uniformity of the projected image.

In view of this, in the liquid crystal projector, a UV cut filter isdisposed in an optical path between the light source and the liquidcrystal display panel, for protecting the liquid crystal display paneland other component parts from UV rays and, further, shorter-wavelengthrays among visible rays which are generated from the light source.

As the UV cut filter, a UV absorptive glass capable of absorbing UV raysor a UV reflective glass comprising a glass substrate provided thereonwith a UV reflection film capable of reflecting UV rays is used.

The UV absorptive glass uses a glass substrate for absorbing UV rays,and the wavelengths to be absorbed (cut) and the leading edgecharacteristic (steepness) of the absorption-to-transmission transitioncan be controlled by selecting the composition of the material and thethickness of the glass substrate.

However, the UV absorptive glass has the problem that the selection ofthe wavelengths to be absorbed is limited by the material of the glasssubstrate and the problem that, since the energy of the absorbed lightis converted into heat, the glass substrate would be broken due to thetemperature rise when strong light is incident on the UV absorptiveglass. This danger has been increasing due to the rise in the energydensity of the light in recent years. In addition, even with thematerial selected and regulated carefully, the transmittance at shortwavelengths near the wavelengths to be cut cannot be much enhanced, sothat attenuation of the light transmitted through the UV absorptiveglass is generated.

On the other hand, in the UV reflective glass, the wavelengths to be cut(reflected) can be arbitrarily selected by conditioning the multi-layerfilm dielectric constituting the UV reflection film, the leading edgecharacteristic is steep, and the transmittance at short wavelengths nearthe wavelengths to be cut can be enhanced.

The UV reflective glass is a kind of multi-layer film cut filter callededge filter. The multi-layer film cut filter has a structure in which amulti-layer film dielectric comprised of an alternate lamination of ahigh-refractive-index layer and a low-refractive-index layer inpredetermined optical film thicknesses (=refractive index n×geometricfilm thickness d) is formed on a light-transmitting substrate by avacuum vapor deposition method etc., and can cut the light ofwavelengths shorter than a specified wavelength and transmitlonger-wavelength light.

However, the UV reflection film composed of the multi-layer filmdielectric is known to be extremely difficult to produce. Specifically,in order to achieve a steeper leading edge characteristic, the number oftimes of film formation in alternately forming the high-refractive-indexlayers and the low-refractive-index layers must be extremely increased;for example, 30 layers or more must be formed. In addition, the filmthickness of each layer is small, particularly in the UV region, and thecontrol of the film thickness of each layer must be conducted with highaccuracy for the purpose of setting the leading edge wavelength withhigh accuracy. It is said that the leading edge wavelength is shifted by5 nm when the film thickness of each layer is shifted by 1%, forexample. According to the film formation technology at present, it isdifficult to control the film thickness with high accuracy and therebyto form a UV reflection film having the characteristics as designed.

Accordingly, a multi-layer film cut filter permitting control of filmthickness with high accuracy and having characteristics as designed anda production method therefor are requested.

Besides, the functions of the UV cut filter in the liquid crystalprojector are to completely shut up UV rays with wavelengths of not morethan 400 nm and a part of visible rays near the UV rays, to preventdeterioration of organic component parts due to such rays, and toprolong the life of the product. In addition, it is demanded to cut apart of blue light from an ultra-high pressure mercury lamp which emitslight excessively rich in blue, and thereby to improve color balance.

Therefore, the UV cut filter for used in the liquid crystal projector isrequired to have a transmittance characteristic adjusted to theluminance characteristic of the ultra-high pressure mercury lamp.However, it has been difficult to say that the conventional UV cutfilter has a transmittance characteristic adjusted to the luminancecharacteristic of the ultra-high pressure mercury lamp. FIG. 17 showsthe luminance characteristic of the ultra-high pressure mercury lamp.

In the luminance characteristic of the ultra-high pressure mercury lampindicated by the thin broken line in the figure, blue light isexcessively much, and the blue light is still strong even if the lightat the peak near 405 nm within the blue wavelength range issubstantially cut, so that the light at the peak near 440 nm mustfurther be cut by about 10 to 30%.

In FIG. 17, one example of the spectral transmittance of a UV absorptiveglass is indicated by the broken line. In addition, one example of thespectral transmittance of a UV reflection film composed of a dielectricmulti-layer film is indicated by the solid line.

The spectral transmittance of the UV absorptive glass is such that thepeak near 405 nm can be substantially completely cut, but the spectraltransmittance is gradual near 440 nm, and it is difficult to enhance thetransmittance at short wavelengths near the wavelengths to be cut.Therefore, there is the problem that attenuation of the lighttransmitted through the UV absorptive glass is generated.

On the other hand, the spectral transmittance of the UV reflection filmhas a steep leading edge. In order to condition the transmittance at thepeak near 440 nm in the UV reflection film, it is necessary to set thehalf-power point (the wavelength at which a transmittance equal to onehalf of the maximum transmittance of the filter is shown) at the leadingedge in the vicinity of 430 nm. The spectral transmittance of the UVreflection film shown in FIG. 17 has a half-power point of 433 nm.

However, the UV reflection film is composed of a multi-layer film of adielectric, and is composed, for example, of a multi-layer film havingno less than 33 layers. As has been described above, the control of filmthickness of each layer must be conducted with high accuracy in order toset the leading edge wavelength with high accuracy, and it is said thatthe leading edge wavelength is shifted by 5 nm when the film thicknessof each layer is shifted by 1%. Under ordinary production conditions,the accuracy of the half-power point, even with best accuracy, is ±4 nm.Therefore, it is extremely difficult to produce a UV reflection filmhaving a half-power point accurately controlled into the vicinity of 430nm, so that there is the problem that the transmittance at the peak near440 nm is largely varied due to a difference in half-power point arisingfrom slight scatter of production conditions.

Accordingly, there is a demand for a UV cut filter capable of securelyhaving a transmittance characteristic adjusted to the luminancecharacteristic of the ultra-high pressure mercury lamp, and a projectiontype display unit using the UV cut filter.

Furthermore, the liquid crystal projectors have shown a tendency towardreductions in size and cost in recent years, and it has been keenlydemanded to reduce the number of component parts. Therefore, there is arequest for a projection type display unit which makes it possible toreduce the UV cut filters as component parts.

The present invention has been made in consideration of theabove-mentioned requests and demands. Accordingly, it is a first objectof the present invention to provide a multi-layer film cut filterpermitting control of film thickness with high accuracy and thereforehaving characteristics as designed.

A second object of the present invention is to provide a method ofproducing a multi-layer film cut filter by which film thickness can beeasily controlled with high accuracy.

A third object of the present invention is to provide a UV cut filterwhich securely has a transmittance characteristic adjusted to theluminance characteristic of an ultra-high pressure mercury lamp.

A fourth object of the present invention is to provide a projection typedisplay unit using a UV cut filter having a transmittance characteristicadjusted to the luminance characteristic of an ultra-high pressuremercury lamp.

A fifth object of the present invention is to provide a dustproof glasswith which UV cut filers as component parts in a projection type displayunit can be reduced.

A sixth object of the present invention is to provide a display panelwith which UV cut filters as component parts in a projection typedisplay unit can be reduced.

A seventh object of the present invention is to provide a projectiontype display unit with which UV cut filters as component parts can bereduced.

SUMMARY OF THE INVENTION

The present inventors have made intensive and extensive investigationsin order to attain the first object. As the result of theirinvestigations, the present inventors have found out that, while arepeated alternate layer in which a high-refractive-index layer and alow-refractive-index layer are alternately and repeatedly laminated oneach other in respectively equal film thicknesses in a dielectricmulti-layer film constituting a UV reflection film functions as a layernecessary for steeply cutting the light of wavelengths shorter than aspecified wavelength, it is effective to change, as compared with theprior art, the balance in thickness between the high-refractive-indexlayer and the low-refractive-index layer in the repeated alternatelayer.

Specifically, as contrasted to the prior art in which the ratio H/L inthe repeated alternate layer has been 1.0, where H is the optical filmthickness of the high-refractive-index layer in the repeated alternatelayer and L is the optical film thickness of the low-refractive-indexlayer, in the present invention the ratio H/L or L/H is set within therange of 1.2 to 2.0.

It has been found out that, when the optical film thickness of one ofthe high-refractive-index layer and the low-refractive-index layer isbiased to be larger and the optical film thickness of the other isbiased to be smaller, the measurement of film thickness by an opticalfilm thickness meter using a film thickness monitor substrate in a filmformation apparatus can be conducted with high accuracy, whereby thefilm thickness can be controlled with high accuracy and the leading edgecharacteristic of the filter obtained becomes better unexpectedly.

For attaining the second object, it has been found out to be effectiveto interposing a correction plate between a vapor source or sources anda light-transmitting substrate in the film formation apparatus and touse a correction plate larger in width than the conventional one so asto increase the proportion of flying particles which are shielded by thecorrection plate. Specifically, where the ratio of the film thickness ofa layer deposited on the light-transmitting substrate to the filmthickness of a layer deposited on the monitor substrate is referred toas tooling coefficient, when the tooling coefficient is set within therange of 0.6 to 0.85, the layer deposited on the monitor substratebecomes thicker than the layer deposited on the light-transmittingsubstrate, so that the measurement of film thickness by the optical filmthickness meter can be conducted with high accuracy, and control of thefilm thickness can be facilitated.

In addition, for attaining the third object, firstly, it has been foundout to be possible to provide the transmittance characteristic of a UVreflection film with a step in average transmittance of 70 to 90% withina wavelength range of 430 to 450 nm. With such a step provided, itsuffices to set the half-power point within the range of 415 to 430 nmso that the peak near 405 nm can be cut; therefore, accuracy is notrequired so much, and such a UV reflection film can be produced easily.Moreover, the transmittance at the peak near 440 nm can be conditionedwith good controllability by the step. By this, it is possible to obtaina UV cut filter having a transmittance characteristic adjusted to theluminance characteristic of the ultra-high pressure mercury lamp.

Secondly, it has been found out to be effective to combine a UVreflection film having a half-power point of 415 to 430 nm with a blueconditioning film having an average transmittance of 70 to 90% within awavelength range of 430 to 450 nm and an average transmittance of atleast 90% within a wavelength range of 430 to 520 nm. With thiscombination, the reflection of UV rays and visible region up to the peaknear 405 nm is carried out by the UV reflection film, and the reflectionof the peak near 440 nm is carried out by the blue conditioning film. Bythis, accuracy of the half-power point of the UV reflection film is notrequired so much, so that the production is facilitated, and thetransmittance of the peak near 440 nm can be conditioned with goodcontrollability by the blue conditioning film. As a result, it ispossible to obtain a UV cut filter having a transmittance characteristicadjusted to the luminance characteristic of the ultra-high pressuremercury lamp.

Thirdly, it has been found out to be effective to combine a UVabsorptive glass having an absorption characteristic with a half-powerpoint of 415 to 430 nm and the above-mentioned blue conditioning film.With this combination, the absorption characteristic of the UVabsorptive glass is compensated for by the blue conditioning film, theabsorption of UV rays and visible region up to the peak near 405 nm iscarried out by the UV absorptive glass, and the transmittance at thepeak near 440 nm can be conditioned with good controllability by theblue conditioning film. By this, it is possible to obtain a UV cutfilter having a transmittance characteristic adjusted to the luminancecharacteristic of the ultra-high pressure mercury lamp.

It has been found out that the fourth object can be attained by aprojection type display unit in which an ultra-high pressure mercurylamp is used as a light source and in which the above-mentioned UV cutfilter having a transmittance characteristic adjusted to the luminancecharacteristic of the ultra-high pressure mercury lamp is used.

In addition, for attaining the fifth object, it has been found out to beeffective to provide a UV reflection film on the front surface of adustproof glass which is disposed on the incidence side of a displayunit constituting a display panel for forming a predetermined image bymodulating light emitted from a light source in a projection typedisplay unit, for preventing dust from being deposited on the displayunit with the result that the deposited dust is projected.

Specifically, a conventional dustproof glass has a structure in which anantireflection coating for enhancing light transmittance is provided onthe front surface of a thick transparent glass substrate. In the case ofa UV reflection film, the wavelengths to be cut can be arbitrarilyselected by regulating the film thickness, and the transmittance atshort wavelengths near the wavelengths to be cut can also be enhanced.Therefore, the UV reflection film has not only the function of cuttingUV rays but also the function as an antireflection coating. Moreover,the UV reflection film reflects most of UV rays and absorbs little of UVrays, so that the temperature of the dustproof glass will not be raised;therefore, there arises no inconvenience when a UV cutting function isgiven to the dustproof glass constituting a display panel. It has thusbeen found out that the antireflection coating of the dustproof glasscan be replaced by the UV reflection film. Then, a projection typedisplay unit using a display panel in which such a dustproof glass isincorporated needs no UV cut filter as a component part, whereby thenumber of component parts can be reduced.

Accordingly, it has been found out that the sixth object can be attainedby incorporating a dustproof glass provided with a UV reflection filminto a display panel, and the seventh object can be attained by usingsuch a display panel in a projection type display unit.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a constitutional view showing the general constitution of aliquid crystal projector using a UV cut filter according to the presentinvention.

FIG. 2 is a constitutional view showing an outline of a physical filmformation apparatus for producing a multi-layer film cut filteraccording to the present invention.

FIG. 3 is a layout view showing the vertical positional relationshipsamong correction plates, a vapor deposition dome, a monitor substrateand vapor sources in the apparatus of FIG. 2.

FIG. 4 is a graph showing the relationship between optical filmthickness and reflectance, of a layer on the monitor substrate.

FIG. 5 is a graph showing the relationship between wavelength andrefractive index, of a layer of TiO₂.

FIG. 6 is a graph showing the spectral transmittances at wavelengthsnear 410 nm of multi-layer film cut filters obtained in Examples 1 and2, and Comparative Examples 1 and 2, respectively.

FIG. 7 is a graph showing the spectral transmittances in a wavelengthrange of 350 to 700 nm of multi-layer cut filters obtained in Examples 1and 2, and Comparative Examples 1 and 2, respectively.

FIG. 8 is a graph showing light quantity variation of an optical monitorin Example 1.

FIG. 9 is a graph showing light quantity variation of an optical monitorin Comparative Example 1.

FIG. 10 is a graph showing spectral transmittances in a wavelength rangeof 350 to 800 nm of a multi-layer film cut filter obtained in Example 3.

FIGS. 11( a) and 11(b) are sectional views showing the sectionalstructures of UV cut filters according to the present invention whicheach have a stepped UV reflection film, and FIG. 11( c) is a graphshowing the spectral transmittances of the UV cut filters.

FIG. 12( a) is a sectional view showing the sectional structure of a UVcut filter according to the present invention in which a UV reflectionfilm and a blue conditioning film are combined, and FIG. 12( b) is agraph showing the spectral transmittance of the UV cut filter.

FIG. 13( a) is a sectional view showing the sectional structure of a UVcut filter according to the present invention in which a UV absorptiveglass and a blue conditioning film are combined, and FIG. 13( b) is agraph showing the spectral transmittance of the UV cut filter.

FIG. 14 is a constitutional view showing the general constitution of aliquid crystal projector as one embodiment of a projection type displayunit according to the present invention.

FIG. 15 is a sectional view showing the sectional structure of oneembodiment of a display panel according to the present invention.

FIGS. 16( a) and 16(b) are sectional views showing embodiments of adustproof glass according to the present invention.

FIG. 17 is a graph showing spectral transmittances of a UV reflectionfilm and a UV absorptive glass.

BEST MODE FOR CARRYING OUT THE INVENTION

Now, embodiments of the present invention will be described below, butthe present invention is not limited to the following embodiments.

First, a multi-layer film cut filter for attaining the first object anda method of producing a multi-layer film cut filter for attaining thesecond object will be described.

The multi-layer film cut filter according to the present invention isone called edge filter, which cuts light of wavelengths shorter than aspecified wavelength and transmits light of longer wavelengths or whichcuts light of wavelengths longer than a specified wavelength andtransmits light of shorter wavelengths. Depending on the function, theedge filter is called UV cut filter, IR cut filter, dichroic filter,cold mirror or the like according to the purpose of use thereof. Such amulti-layer film cut filter is used for cutting or separating unrequitedor harmful high-order frequency (short wavelength) light, in variousoptical measurements or in projection systems, image pickup systems orlaser processing systems.

The principal use of the multi-layer film cut filter according to thepresent invention is the use as a UV cut filter, which is disposedbetween an optical component part exposed to a source of lightcontaining strong UV rays such as a high-output mercury lamp in aprojection type display unit such as a liquid crystal projector, a rearprojection unit, television, a projection type display, etc. and thelight source, for the purpose of cutting UV rays and a part ofshort-wavelength visible rays emitted from the light source so as toprotect the optical component part. The projection type display unit isa system in which the light from the light source is modulated to form apredetermined image at a display panel, and the light emitted from thedisplay panel is enlargedly projected onto a screen by anenlarged-projection optical system. In the case of performing a colordisplay, the light from the light source is spectrally split into red,green and blue wavelength bands, which are inputted to and modulated atthe display panel, and the modulated color components are synthesized soas to display a color image.

FIG. 1 shows the general constitution of a liquid crystal projector. Inthe liquid crystal projector 100, the light from a light source 101 isspectrally split into three primary colors, i.e., red R, green G, andblue B by a blue-green reflective dichroic mirror 111 and a greenreflective dichroic mirror 112, then the red color is passed through afirst liquid crystal display panel 121, the green color is passedthrough a second liquid crystal panel 122, and the blue color is passedthrough a third liquid crystal display panel 123 via a polarizing plateunit 131. These liquid crystal display panels 121, 122, and 123 arecalled light bulbs, and the same image is displayed thereon. The lightcomponents modulated by passing through the liquid crystal displaypanels 121, 122, and 123 are synthesized into a color image by adichroic prism 140, and the color image is projected by a projectionlens 150 functioning as an enlarged-projection optical system.

As the light source 101, in recent years, an ultra-high pressure mercurylamp having an extremely high luminance has been used in many cases. Theultra-high pressure mercury lamp is used also as a UV source, and thelight emitted therefrom contains UV components (not more than 400 nm inwavelength) in a very high proportion, as shown in FIG. 17.

While the light components transmitted through the dichroic mirrors 111and 112 are incident on the first liquid crystal display panel 121 andthe second liquid crystal display panel 122, these light components donot contain the UV component since the UV component is contained in theblue color B, and, therefore, these liquid crystal display panels 121and 122 need no particular measures against UV rays. The UV rays emittedfrom the light source 101 is primarily incident on the third liquidcrystal panel 123.

In an ordinary liquid crystal projector, a UV cut filter 10 is disposedon an optical path on the upstream side of the polarizing plate unit 131disposed on the upstream side of the third liquid crystal display panel123 for modulating blue color, in order to protect these component partsfrom UV rays. The position at which the UV cut filter 10 is disposed isnot limited to that shown in FIG. 1, but may be any position on theoptical path from the light source 101 to the third liquid crystaldisplay panel 123. Besides, the UV cut filter may not necessarily beprovided as an independent component part, and, for example, thefunction as the UV cut filter may be added to a lens disposed on theoptical path.

The multi-layer film cut filter used as the UV cut filter 10 has astructure in which a dielectric multi-layer film composed of analternate lamination of a high-refractive-index layer and alow-refractive-index layer is formed as a UV reflection film on alight-transmitting substrate.

The light-transmitting substrate may be formed of a material whichtransmits rays, and, ordinarily, an inorganic glass is used as thematerial. Examples of the material for this use include soda lime glass,borosilicate glass, lead glass, alkali-free glass, quartz glass,Neoceram, 7971 titanium silicate glass (a product by Corning), sapphireglass, etc.

The shape of the light-transmitting substrate is ordinarily a sheet-likeshape, but, for example, an optical lens used in a projection typedisplay unit can be used as the substrate of the UV cut filter accordingto the present invention.

As the material of the high-refractive-index layers of the dielectricmulti-layer film constituting the UV reflection film, there may be usedTiO₂ (n=2.4), Ta₂O₅ (n=2.1), Nb₂O₅ (n=2.2) or the like. As the materialof the low-refractive-index layers, there may be used SiO₂ (n=1.46) orMgF₂ (n=1.38). The refractive index varies depending on wavelength, andthe just-mentioned values of refractive index n are values at awavelength of 500 nm.

The basic design of film thickness is generally represented by, forexample, the formula (0.5H, 1L, 0.5H)^(s), as a repeated alternate layerin which a high-refractive-index layer and a low-refractive-index layerare repeatedly and alternately laminated on each other in respectivelyequal optical film thicknesses. Here, the wavelength near the center ofthe wavelengths to be cut is made to be a design wavelength λ, the filmthickness of the high-refractive-index layer (H) is represented as 1H bytaking the optical film thickness nd=¼λ as a unit, and the filmthickness of the low-refractive index layer (L) is similarly representedas 1L. S in the formula is called stack number, which is the number oftimes of repetition, meaning that the constitution parenthesized in theformula is periodically repeated. The number of the layers actuallylaminated is 2S+1, and, when the value of S is enlarged, the leadingedge characteristic (steepness) of the reflection-to-transmissiontransition can be made steeper. The value of S is selected from therange of about 3 to 20. By the repeated alternate layer, the specifiedwavelength for the cutting of light is determined.

In order to enhance the transmittance in a transmission band and tochange the ruggedness of transmittance called ripples into a flatcharacteristic, an optimum designing is conducted by varying the filmthickness of several layers near the substrate and several layers nearthe medium, of the repeated alternate layer. Therefore, the design isrepresented for example by the expression: substrate|0.5LH . . .HL(HL)^(s)HL . . . H, 0.5L. In addition, where TiO₂ or the like is usedfor forming the high-refractive-index layers, it is a common practice todesign the repeated alternate layer by adding a layer of SiO₂, which isexcellent in environmental resistance, as an outermost layer, ratherthan terminating with the high-refractive-index layer as the outermostlayer. As for the layer in contact with the substrate, also, a layer ofSiO₂, which is chemically stable, may be added as the first layer, sinceTiO₂ might react with the substrate with the result of deterioration ofcharacteristics. Such a designing of the multi-layer film cut filter canbe theoretically conducted by use of a commercial software (reference:OPTRONICS, 1999, No. 5, pp. 175–190).

In order to form the high-refractive-index layers and thelow-refractive-index layers alternately on the light-transmittingsubstrate, a physical film formation method is generally used. While anordinary vacuum vapor deposition method may be used, it is preferable touse ion-assisted vapor deposition, an ion plating method, or asputtering method, by which it is possible to stably control therefractive indexes of the films and to form films less susceptible totime changes in optical characteristics due to storage, specificationand environmental variations. The vacuum vapor deposition method is amethod in which a thin film material is evaporated by heating in a highvacuum, and the particles of the evaporated material are deposited on asubstrate to form a thin film. The ion plating method is a method inwhich vapor-deposition particles are ionized, and the ionized particlesare accelerated by an electric field, to be deposited on a substrate.Systems of the ion plating method include APS (Advanced Plasma Source),EBEP (Electron Beam Excited Plasma) method, and RF (Radio Frequency)direct substrate opration method (reactive vapor deposition is conductedin the condition where a high-frequency gas plasma is generated in afilm formation chamber). The sputtering method is a thin film formingmethod in which a thin film material is evaporated by sputtering, whichis a process for beating out the thin film material by impingingfield-accelerated ions against the thin film material, and the particlesof the evaporated material are deposited on a substrate. The opticalconstants such as refractive index of the layer thus formed varydepending on the film formation method, film formation conditions, etc.,so that it is necessary to accurately measure the optical constants ofthe layer to be formed, before production.

FIG. 2 shows one example of a physical film formation system using anoptical film thickness meter which is widely used for control of filmthickness. The physical film formation system 200 comprises a filmformation apparatus 210 and the optical film thickness meter 220. Twovapor sources 212 and 213 in which thin film materials, i.e., ahigh-refractive-index material and a low-refractive-index material arerespectively charged in crucibles are disposed at lower portions insidea vacuum chamber 211 constituting the film formation apparatus 210. Thevapor sources 212 and 213 can be subjected to heating or sputtering byvarious methods. A dome-shaped vapor deposition dome 214 for mounting alight-transmitting substrate thereon is rotatably supported at an upperportion inside the vacuum chamber 211. A substrate heater 215 forheating the vapor deposition dome 214 is disposed on the upper side ofthe vapor deposition dome 214. A hole for monitoring is bored in acentral portion of the vapor deposition dome 214, and a monitorsubstrate 221 for monitoring film thickness, which constitutes theoptical film thickness meter 220, is disposed at the hole. The monitorsubstrate 221 is composed of a monitor glass. Light emitted from a lightprojector 222 is incident on a film formation surface of the monitorsubstrate 221, the light reflected by the film formation surface isreceived by a light receiving unit 223 and is converted into an electricsignal, which is transmitted to a measuring unit 224, which measures thequantity of reflected light, and the reflected light quantity isoutputted to a recorder 225. Correction plates 216 for correcting filmthickness distribution are fixedly disposed between the vapor sources212, 213 and the vapor deposition dome 214.

FIG. 3 shows vertical positional relationships among the correctionplates 216, the vapor deposition dome 214, the vapor sources 212 and213, and the monitor substrate 221. The two correction plates 216 arefixed respectively on the upper side of the vapor sources 212 and 213,whereas the vapor deposition dome 214 is rotated. Of the particlesflying from the vapor source 212, 213, the high-concentration portion isprevented from reaching the vapor deposition dome 214 by the correctionplate 216; therefore, the distribution of the particles flying to thevapor deposition dome 214 can be made uniform by the correction plate216. The correction plates 216 do not inhibit the flying particles fromreaching the monitor substrate 221, and, therefore, the correctionplates 216 have the function of conditioning the proportion of the filmthickness of the layer formed on the vapor deposition dome 214 and thefilm thickness of the layer formed on the monitor substrate 221.

The particles of the thin film material evaporated from the vapor source212, 213 are accelerated by an electric field (not shown) beforereaching the vapor deposition dome 214 in the case of ion plating, ordirectly reach the vapor deposition dome 214 in the case of vacuum vapordeposition. The particles reach the light-transmitting substrate mountedon the vapor deposition dome 214 being rotated, and are deposited on thelight-transmitting substrate, to form an optical film on thelight-transmitting substrate. In this case, the portion high in particledensity of the thin film material is blocked by the correction plate216, so that a uniform film thickness distribution can be obtained. Byswitching the vapor source 212 on one side and the vapor source 213 onthe other side, the two kinds of thin film materials can be deposited toform layers alternately. The two kinds of thin film materials aredeposited to form layers alternately on the monitor substrate 221,simultaneously with the film formation on the light-transmittingsubstrate.

The optical film thickness meter 220 continuously measure, during filmformation, the variation in the quantity of light reflected ortransmitted at a designated wavelength (selected from the wavelengthrange usable with the film thickness sensor) by use of the filmdeposited on the monitor substrate 221, and the film formation isfinished when a preliminarily computed light quantity change hasoccurred. The light quantity variation on the monitor substrate 221shows peaks while repeating an increase and a decrease periodically eachtime the optical film thickness reaches an integer times of ¼ of themeasurement wavelength λ, as shown in FIG. 4. Therefore, by determiningthe film formation amount based on such a peak, the actual optical filmthickness can be controlled accurately, and, for this reason, theoptical film thickness meter 220 is widely used for formation of anoptical thin film.

However, in the case of UV cutting, it is necessary to select a shortwavelength as the design wavelength, and the film thickness of eachlayer is extremely small, so that it is difficult to control the filmthickness. In addition, in the UV region, there is the problem that theaccuracy of measurement becomes unstable because of large variations ofoptical constants such as refractive index of the substrate and thefilm, as seen from FIG. 5 which shows variation in the refractive indexof TiO₂ with wavelength. Furthermore, in the film formation system usingthe optical film thickness meter, there arises the problem that thevariation in light quantity becomes flat in the vicinity of a lightquantity variation peak, so that it is difficult to decide the lightquantity variation peak, and accuracy of control is conspicuouslydegraded. Moreover, where TiO₂ is used, the measurement of lightquantity variation itself becomes difficult due to absorption by TiO₂,so that the accuracy of film formation is extremely worsened. Further,when the repetition number S is increased for realizing a steep leadingedge characteristic, it becomes further more difficult to form the filmintended. Conventionally, therefore, it has been impossible to achievemass production where the stack number S is at least 10.

In the present invention, the difficulties in film thickness control atthe time of film formation in the production of the UV cut filter asabove-mentioned are overcome by making contrivances as to the balance offilm thicknesses in the repeated alternate layer and the size of thecorrection plate, whereby it is made possible to control film thicknesswith high accuracy and to carry out mass production.

To be more specific, in the conventional designing, the ratio H/L ofoptical film thicknesses in the repeated alternate layer is set at 1.0.Where the ratio H/L is 1.0, the film formation must be stoppedaccurately when the reflectance on the monitor substrate reaches a peak,corresponding to an integer times of λ/4. In this case, the variation inlight quantity becomes flat in the vicinity of the light quantityvariation peak as measured by the optical film thickness meter, so thatit is difficult to decide the light quantity variation peak.

In contrast, in the present invention, the ratio H/L or L/H in therepeated alternate layer is set within a range of from 1.2 to 2.0,preferably from 1.3 to 1.5; namely, a bias in thickness is introduced bysetting one of the high-refractive-index layer and the low-refractiveindex layer to be thicker and the other to be thinner. In this case, ifthe bias is too heavy, a bad influence may be exerted on the filtercharacteristics.

As a result of the foregoing, at the time of forming the thicker layer,film formation is stopped when the peak of light quantity variation inthe optical film thickness meter has been passed way, so that the timingfor stopping the film formation becomes clear, and control of filmthickness is facilitated. In addition, as for the control of filmthickness of the thinner layer, the thinner layer is formed on thethicker layer and, therefore, film formation is stopped at the peak asusual; thus, no inconvenience arises from the setting of the layer to bethinner. Among others, by setting the high-refractive-index layer to bethicker, it is possible to form, with good film thickness accuracy, thehigh-refractive-index layer which has a small geometric film thicknessand the film thickness of which is difficult to control.

Next, in the present invention, the width of the correction plate 216 isset to be larger than usual, whereby the proportion of the flyingparticles shielded by the correction plate 216 is increased.Specifically, where the ratio of the film thickness of the layerdeposited on the light-transmitting substrate to the film thickness ofthe layer deposited on the monitor substrate is referred to as toolingcoefficient, the tooling coefficient is set within a range of 0.6 to0.85. When the tooling coefficient is too low, the amount of theparticles deposited on the light-transmitting substrate will be toosmall, which is unfavorable from the viewpoint of productivity. Theordinary tooling coefficient in a conventional film formation apparatusis generally within a range of 0.9 to 1.1.

As a result of this, the layer deposited on the monitor substrate 221becomes thicker than that deposited on the light-transmitting substrate,and the film thickness thereof can be measured accurately, therebymaking it possible to solve the problem that optical constants such asrefractive index would be unstable in the UV region. In addition, thepeak of light quantity variation at the monitor substrate 221 precedesthe peak in film formation on the light-transmitting substrate and,therefore, the film formation can be stopped when the peak in the lightquantity variation has been passed way, so that the timing for stoppingthe film formation is made clear, and control of film thickness isfacilitated. As a result, accuracy of film thickness can be enhanced.

By a combination of the improvement in the film thickness balance in therepeated alternate layer with the improvement of setting the toolingcoefficient to be lower by setting the width of the correction plate tobe larger, there is obtained an additional effect that film formation informing the lower-refractive-index layer can be stopped when the peak oflight quantity variation in the optical film thickness meter has beenpassed away, whereby control of film thickness is further facilitated.

Where the multi-layer film cut filter with the ratio H/L or L/H in therepeated alternate layer set within a range of 1.2 to 2.0 according tothe present invention is used as a UV cut filter, the half-power pointof leading edge is preferably selected within a wavelength range of 400to 450 nm so that UV rays and short-wavelength visible rays can be cut.Particularly, where an ultra-high pressure mercury lamp is used as alight source, for improving the color balance of the light source it ispreferable to set the half-power point within a range of 425 to 440 nm,particularly in the vicinity of 430 to 435 nm so that the peak near 440nm of the light from the ultra-high pressure mercury lamp can be partlyreflected by 10 to 30%, preferably about 10 to 20%.

On the side opposite to the side where the UV reflection film isprovided of the light-transmitting substrate of the UV cut filter, anordinary antireflection coating for enhancing light transmittance may beformed.

The multi-layer film cut filter according to the present invention isapplicable to all filters that have a structure in which a dielectricmulti-layer film comprising a repeated alternate film is formed on alight-transmitting substrate. Naturally, the multi-layer film cut filteraccording to the present invention is applicable not only to a UV cutfilter but also to an IR cut filter, a dichroic filter, a cold mirror,etc.

EXAMPLE 1

The ratio H/L of film thicknesses in a repeated alternate layer was setat about 1.33, thereby setting a thickness balance to make the H layersthicker. The outermost layer and the first layer in contact with asubstrate were formed of SiO₂.

As the material of the light-transmitting substrate, BK7 (a colorlessglass plate with n=1.52) was used. As for the materials to constitutelayers, TiO₂ was used for high-refractive-index layers (H), while SiO₂was used for low-refractive-index layers (L), and film formation wasconducted by use of an RF ion plating apparatus (a product by SHOWASHINKU CO., LTD.). An optical film thickness meter of the monochromaticoptical monitor system was used. Correction plates larger in width thanusual was used, and the tooling coefficient was set at 0.8.

As for film thickness constitution, λ=360 nm, the number of layers was33, and the multi-layer design was 1.08L, 0.44H, 1.04L, 0.88H, 0.80L,1.16H, 0.76L, (1.12H, 0.84L)¹⁰, 1.00H, 0.92L, 1.16H, 0.60L, 1.04H,1.80L, in this order from the substrate side.

An enlarged spectral transmittance in the vicinity of a wavelength of410 nm of the multi-layer film cut filter obtained is shown in FIG. 6.Besides, a spectral transmittance within a wavelength range of 350 to700 nm is shown in FIG. 7.

In addition, the variation of reflectance measured by the optical filmthickness meter for the repeated laminate layer is shown in FIG. 8. Inthe figure, the solid line corresponds to the film formation of thehigh-refractive-index layer, and the one-dotted chain line correspondsto the film formation of the low-refractive-index layer. The right endof each of the lines shows that the film formation was stopped at thattime point.

EXAMPLE 2

Under the same film formation conditions as in Example 1, the filmthickness constitution was so set that λ=360 nm, the number of layerswas 19, and the multi-layer design was 1.08L, 0.44H, 1.04L, 0.88H,0.80L, 1.16H, 0.76L, (1.12H, 0.84L)³, 1.00H, 0.92L, 1.16H, 0.60L, 1.04H,1.80L, in this order from the substrate side.

An enlarged spectral transmittance in the vicinity of a wavelength of410 nm of the multi-layer film cut filter obtained is shown in FIG. 6.Besides, a spectral transmittance within a wavelength range of 350 to700 nm is shown in FIG. 7.

This layer constitution is characterized in that the number of layerswas reduced in consideration of productivity, and since the stack numberin the repeated alternate layer was small, the steepness of the spectralcharacteristic was lowered.

COMPARATIVE EXAMPLE 1

Under the same film formation conditions as in Example 1, optimizationaccording to the conventional design was conducted. The film thicknessconstitution was such that λ=360 nm, the number of layers was 33, andthe multi-layer design was 1L, 0.3H, 0.94L, 1.1H, 0.58L, 1.3H, 0.79L,(1H, 1L)¹⁰, 1.02H, 0.71L, 1.74H, 0.32L, 1.35H, 1.68L, in this order fromthe substrate side.

An enlarged spectral transmittance in the vicinity of a wavelength of410 nm of the multi-layer film cut filter obtained is shown in FIG. 6.Besides, a spectral transmittance within a wavelength range of 350 to700 nm is shown in FIG. 7.

In addition, the variation of reflectance measured by the optical filmthickness meter for the repeated alternate layer is shown in FIG. 9. Inthe figure, the solid line corresponds to the film formation of thehigh-refractive-index layer, while the one-dotted chain line correspondsto the film formation of the low-refractive-index layer. The right endof each of the lines shows that the film formation was stopped at thattime point.

COMPARATIVE EXAMPLE 2

Under the same film formation conditions as in Example 1, the filmthickness constitution was so set that λ=360 nm, the number of layerswas 19, and the multi-layer design was 1L, 0.3H, 0.94L, 1.1H, 0.58L,1.3H, 0.79L, (1H, 1L)³, 1.02H, 0.71L, 1.74H, 0.32L, 1.35H, 1.68L, inthis order from the substrate side.

An enlarged spectral transmittance in the vicinity of a wavelength of410 nm of the multi-layer film cut filter obtained is shown in FIG. 6.Besides, a spectral transmittance within a wavelength range of 350 to700 nm is shown in FIG. 7.

Since the number of layers is small, the production of the multi-layerfilm cut filter was somewhat easy, but the steepness of spectralcharacteristic was poor.

Example 1 and Comparative Example 1 are equal in the number of layers,but are different in the balance of film thicknesses in the repeatedalternate layer. Example 1 gave a steeper spectral characteristic.Similarly, Example 2 and Comparative Example 2 are equal in the numberof layers, but are different in the balance of film thicknesses in therepeated alternate layer, and Example 2 gave a steeper spectralcharacteristic.

In addition, the variation in optical monitor light quantity shown inFIG. 9 shows that, in the film formation of the high-refractive-indexlayer in the repeated alternate layer according to the prior art withH/L=1.00, the film formation must be stopped at the crest of a peak, sothat the decision of the timing for stopping the film formation isdifficult to make, and control of film thickness is difficult toachieve. On the other hand, it is shown that, in forming thelow-refractive-index layer, the film formation can be stopped when apeak has been passed way, owing to the effect of setting the toolingcoefficient at 0.8, so that control of film thickness is easy to carryout.

In contrast, the variation in optical monitor light quantity in thepresent invention in which the balance of film thicknesses in therepeated alternate layer was set at H/L=1.33 as shown in FIG. 8 showsthat, in forming the high-refractive-index layer, the film formation canbe stopped when a peak has been passed way, so that control of filmthickness is easy to carry out. It is also shown that, in forming thelow-refractive-index layer, the film formation can be stopped when apeak has been passed way, owing to the effect of setting the toolingcoefficient at 0.8, so that control of film thickness is easy to carryout.

EXAMPLE 3

A UV cut filter comprising a UV reflection film provided on one side ofa light-transmitting substrate and an antireflection coating provided onthe other side of the light-transmitting substrate was produced. Theratio H/L of film thicknesses in the repeated alternate layer was set atabout 1.31, thereby setting a thickness balance to make the H layersthicker. The outermost layer and the first layer in contact with thesubstrate were formed of SiO₂.

As the material of the light-transmitting substrate, BK7 (a colorlessglass plate with n=1.52) was used. As for the materials of layers, TiO₂was used for high-refractive-index layers (H), while SiO₂ was used forlow-refractive-index layers (L), and film formation was conducted by useof an RF ion plating apparatus (a product by SHOWA SHINKU CO., LTD.). Anoptical film thickness meter of the monochromatic optical monitor systemwas used. Correction plates broader than usual were used, and thetooling coefficient was set at 0.8.

The film thickness constitution was so set that the designwavelength=371 nm, the number of layers was 33, and the multi-layerdesign was 1L, 0.36H, 1.21L, 0.74H, 0.97L, 1.08H, 0.87L, 1.08H, (0.88L,1.15H)⁸, 0.88L, 1.12H, 0.9L, 1.01H, 1.02L, 1.03H, 0.71L, 1.09H, 1.75L,in this order from the substrate side. The half-power point is 433 nm.

In addition, as the antireflection coating, one having an ordinaryfour-layer constitution was formed. The film constitution was 0.23H,0.4L, 2.17H, 1L, in this order from the substrate side (designwavelength: 550 nm).

A spectral transmittance of the multi-layer film cut filter obtained isshown in FIG. 10. In the figure, the one-dotted chain line indicates thespectral transmittance of the multi-layer film cut filter obtained, andthe broken line indicates the spectral transmittance of one example ofUV absorptive glass. In addition, the thin broken line indicates theluminance distribution of an ultra-high pressure mercury lamp.

In Example 3 as shown in FIG. 10, a spectral transmittance adjusted tothe luminance characteristic of the ultra-high pressure mercury lamp wasobtained. Specifically, the luminance characteristic of the ultra-highpressure mercury lamp shown in FIG. 10 is chacterized in that it issomewhat excessively rich in blue light, and, when only the light at thepeak near 405 nm in the blue wavelength region is substantially cut, theblue light is still strong. Therefore, it is necessary to further cutthe light near a wavelength of 440 nm, preferably the light within awavelength range of 430 to 450 nm, by about 10 to 30%.

The transmittance characteristic of the UV absorptive glass is suchthat, although the peak near 405 nm can be cut substantially completely,it is difficult to enhance the transmittance at short wavelengths nearthe wavelengths to be cut because the transmittance variation is gradualin the vicinity of 440 nm. Therefore, attenuation of the lighttransmitted is generated. In addition, it is difficult to cut the lightin a wavelength range of 430 to 450 nm by about 10 to 30%.

The multi-layer film cut filter obtained in Example 3, shown in FIG. 10,has a half-power point of 433 nm. Therefore, the peak near 405 nm can becut substantially completely, and, at the same time, the light in awavelength range of 430 to 450 nm can be cut by about 10 to 30%. Bythis, it is possible to cut a part of blue light emitted from theultra-high pressure mercury lamp, which is excessively rich in blue, andthereby to improve the color balance. Moreover, since the leading edgeis steep, it is possible to enhance the transmittance at shortwavelengths near the wavelengths to be cut.

Next, a UV cut filter for attaining the third object and a projectiontype display unit for attaining the fourth object will be described.

The purposes of the UV cut filter 10 to be used in the projection typedisplay unit 100 is to cut substantially completely UV rays atwavelengths of not more than 400 nm and a part of visible rays near theUV rays, to prevent deterioration of organic component parts by theserays, to prolong the life of the product, and, in the case of using anultra-high pressure mercury lamp as a light source 101, to cut a part ofblue light emitted from the ultra-high pressure mercury lamp, which isexcessively rich in blue, and thereby to improve the color balance. TheUV cut filter according to the present invention is characterized inthat it has a transmittance characteristic adjusted to the luminancecharacteristic of the ultra-high pressure mercury lamp. Specifically,when only the light at the peak near 405 nm within the blue wavelengthrange of the ultra-high pressure mercury lamp shown in FIG. 17 issubstantially cut, the blue light is still strong. In view of this, theUV cut filter according to the present invention further cuts partly thelight at the peak near 440 nm by about 10 to 30%, preferably about 10 to20%.

A first embodiment of the UV cut filter according to the presentinvention will be described referring to FIGS. 11( a) to 11(c).

The UV cut filter 10 a according to the first embodiment shown in FIG.11( a) has a structure in which a stepped UV reflection film 12 isprovided on one side of a light-transmitting substrate 11, and anantireflection coating 13 is provided on the other side of thelight-transmitting substrate 11. On the other hand, the UV cut filter 10b according to the first embodiment shown in FIG. 11( b) has a structurein which a stepped UV reflection film 12 is provided on one side of alight-transmitting substrate 11, and no film is provided on the otherside of the light-transmitting substrate 11.

As the light-transmitting substrate 11, one formed of a material whichtransmits visible rays may be used, and an inorganic glass is generallyused as the material. Examples of the material which may be used includesoda lime glass, borosilicate glass, lead glass, alkali-free glass,quartz glass, Neoceram, 7971 titanium silicate glass (a product byCorning), sapphire glass, etc.

The shape of the light-transmitting substrate 11 is generally asheet-like shape, but, for example, an optical lens used in a projectiontype display unit can be used as the substrate of the UV cut filteraccording to the present invention.

For adjustment to the luminance characteristic of an ultra-high pressuremercury lamp, the transmittance characteristic of the stepped UVreflection film 12 is desirably such that it has a half-power point of415 to 430 nm, an average transmittance of 70 to 90%, preferably anaverage transmittance of 80 to 90% in a wavelength range at the step of430 to 450 nm, and a transmittance of at least 90%, preferably at least95% in a wavelength range of 460 to 520 nm.

The stepped UV reflection film 12 having such a transmittancecharacteristic is a kind of above-mentioned multi-layer film cut filter,so that it can be designed by use of a commercial software for designinga multi-layer film structure.

In addition, for control of film thickness with high accuracy, thestepped UV reflection film 12 preferably has a ratio H/L or L/H in therepeated alternate layer within a range of 1.2 to 2.0, preferably 1.3 to1.5, similarly to the multi-layer film cut filter according to thepresent invention. Further, at the time of physical film formation, itis preferable to interpose correction plates between vapor sources andthe light-transmitting substrate, whereby a tooling coefficient, i.e.,the ratio of the film thickness of the layer deposited on thelight-transmitting substrate to the film thickness of the layerdeposited on a monitor substrate is set within a range of 0.6 to 0.85.

The spectral transmittance of a stepped UV reflection film actuallyformed on BK7 (a colorless glass plate with n=1.52) in Example 4 whichwill be described later is indicated by the solid line {circle around(1)} in FIG. 11( c). In the figure, the broken line {circle around (7)}indicates the luminance characteristic of an ultra-high pressure mercurylamp.

The stepped UV reflection film having the spectral transmittance {circlearound (1)} is a 37-layer film filter composed of alternate laminationof TiO₂—SiO₂. The stepped UV reflection film has a half-power point of425 nm, and an average transmittance of about 85% within a wavelengthrange (step) of 428 to 450 nm. The stepped UV reflection film has a hightransmittance of at least 95% within a wavelength range of 460 to 520nm.

Such a stepped UV reflection film may have a half-power point in therange of 415 to 430 nm, and, since the allowable range of the half-powerpoint is thus broad, the production thereof is easy. If the half-powerpoint is lower than 415 nm, the peak near 405 nm of the ultra-highpressure mercury lamp cannot be cut sufficiently, so that it isdifficult to prevent deterioration of component parts. On the otherhand, when the half-power point is higher than 430 nm, scatter ofhalf-power point on a production basis leads to an influence on thetransmittance at the peak near 440 nm, thereby loosing the meaning ofthe provision of the step.

Besides, the wavelength range of the step is set to be 430 to 450 nm, inorder to condition the transmittance at the peak near 440 nm of theultra-high pressure mercury lamp, thereby to suppress blue color and tocondition the color balance. The average transmittance at the step isset in the range of 70 to 90%, preferably 80 to 90%, in view of the needto set the transmittance within such a range from the viewpoint of colorbalance.

Furthermore, it is necessary for the stepped UV reflection film to havea transmittance of at least 90%, preferably at least 95% in a wavelengthrange of 460 to 520 nm, since it is necessary to brighten the projectedlight by preventing the luminance of the light source from beinglowered.

The antireflection coating 13 provided in the UV cut filter 10 a shownin FIG. 11( a) has the function of suppressing the reflection on thesurface of the light-transmitting substrate 11, thereby enhancing thetransmittance for visible rays.

The antireflection coating 13 is composed of a single layer or amultiplicity of layers of an inorganic or organic film or films.Examples of the material of the inorganic film or films includeinorganic materials such as SiO₂, SiO, ZrO₂, TiO₂, TiO, Ti₂O₃, Ti₂O₅Al₂O₃, Ta₂O₅, CeO₂, MgO, Y₂O₃, SnO₂, MgF₂, WO₃, etc., which may be usedsingly or in combination of two or more thereof. In addition, in thecase of a multi-layer film structure, high-refractive-index layers andlow-refractive-index layers are alternately laminated on each other. Inthe case of the multi-layer film structure, the outermost layer ispreferably formed of SiO₂, which is excellent in environmentalresistance characteristic.

As a method for forming the inorganic film or films, there may beadopted, for example, a vacuum vapor deposition method, an ion platingmethod, a sputtering method, a CVD method, a method of depositing aninorganic material by a chemical reaction in a saturated solution, etc.An organic film or films can be formed not only by a vacuum vapordeposition method but also by coating methods such as a spin coatingmethod, a dip coating method, etc.

The antireflection coating can also be theoretically designed by use ofa commercial software, in the same manner as in designing themulti-layer film cut filter mentioned above.

The UV cut filter 10 a shown in FIG. 11( a), comprising the stepped UVreflection film 12 and the antireflection coating 13, can be used as anindependent UV cut filter because it is provided with the antireflectioncoating 13.

Besides, the UV cut filters 10 a and 10 b do not substantially absorb UVrays and are therefore free of heat generation, so that they can be usedalso as a dustproof glass for use in a liquid crystal display panel.

The UV cut filters 10 a and 10 b thus provided with the stepped UVreflection film 12 can reflect the UV rays and visible rays atwavelengths shorter than the peak near 405 nm of the ultra-high pressuremercury lamp by the appropriate setting of the half-power point, and cancondition the transmittance for the peak near 440 nm by the step.Therefore, with the UV cut filters 10 a and 10 b, it is possible toprevent the deterioration of component parts by UV rays, to securelyreduce the excessively rich blue color of the ultra-high pressuremercury lamp, and thereby to condition the color balance.

Next, a second embodiment of the UV cut filter according to the presentinvention will be described referring to FIGS. 12( a) and 12(b).

As shown in FIG. 12( a), the UV cut filter 10 c according to the secondembodiment has a structure in which a UV reflection film 14 is providedon one side of a light-transmitting substrate 11, and a blueconditioning film 15 as a reflective film for blue color is provided onthe other side of the light-transmitting substrate 11.

The UV reflection film 14 in the UV cut filter 10 c has a transmittancecharacteristic with a half-power point of 415 to 430 nm, and has thefunction of reflecting UV rays and visible rays at wavelengths shorterthan the half-power point. If the half-power point is lower than 415 nm,the peak near 405 nm of the ultra-high pressure mercury lamp cannot becut sufficiently, resulting in that it is difficult to preventdeterioration of component parts. When the half-power point is set to behigher than 430 nm, scatter of half-power point on a production basisleads to an influence on the transmittance at the peak near 440 nm,thereby loosing the meaning of the provision of the blue conditioningfilm. The UV reflection film 14 can be produced easily, since theallowable range for the half-power point is as broad as from 415 to 430nm.

In addition, it is necessary for the blue conditioning film 15 to havethe function of conditioning the transmittance at the peak near 440 nmof the ultra-high pressure mercury lamp, to have an averagetransmittance of 70 to 90%, preferably 80 to 90% in a wavelength rangeof 430 to 450 nm, and to have a transmittance of at least 90%,preferably at least 95% in a wavelength range of 460 to 520 nm. Theaverage transmittance in the wavelength range of 430 to 450 nm is set tobe 70 to 90%, preferably 80 to 90%, in view of the need to set thetransmittance at the peak near 440 nm of the ultra-high pressure mercurylamp to within such a range from the viewpoint of color balance.Besides, it is necessary for the blue conditioning film 15 to have atransmittance of at least 90%, preferably at least 95% in the wavelengthrange of 460 to 520 nm, since it is necessary to brighten the projectedlight by preventing the luminance of the light source from beinglowered.

The blue conditioning film 15 is constituted of a dielectric multi-layerfilm comprising an alternate lamination of a high-refractive-index layerand a low-refractive-index layer provided on a light-transmittingsubstrate. It should be noted here that, in the blue conditioning film15, the number of layers laminated is much smaller than that in the UVreflection film, and there is no repeated alternate layer. The blueconditioning film 15 also can be designed by use of a commercialsoftware for designing the multi-layer film cut filter mentioned above.

The spectral transmittance of the UV reflection film 14 actually formedon BK7 in Example 5 which will be described later is indicated by thebroken line {circle around (2)} in FIG. 12( b), and the spectraltransmittance of the blue conditioning film 15 is indicated by theone-dotted chain line {circle around (3)} in FIG. 12( b). The spectraltransmittance of the UV cut filter 10 c comprising the combination ofthese films is indicated by the solid line {circle around (4)}. In thefigure, the broken line {circle around (7)} indicates the luminancecharacteristic of the ultra-high pressure mercury lamp.

The UV reflection film 14 having the transmittance characteristic shownin FIG. 12( b) is a 33-layer film composed of an alternate lamination ofTiO₂—SiO₂ and having a half-power point of 425 nm. The blue conditioningfilm 15 is a 9-layer film of TiO₂—SiO₂, having an average transmittancein a wavelength range of 430 to 450 nm of about 85% and a transmittanceof at least 96% in a wavelength range of 460 to 520 nm.

Since the half-power point of the UV reflection film 14 is 425 nm, thetransmittance of the blue conditioning film 15 is predominant in thewavelength range of 430 to 450 nm, and, therefore, the transmittance ofthe UV cut filter 10 c in the wavelength range of 430 to 450 nm isapproximate to the transmittance of the blue conditioning film 15.

The UV cut filter 10 c comprising the combination of the UV reflectionfilm 14 and the blue conditioning film 15 as above can reflect UV raysand visible rays at wavelengths shorter than the peak near 405 nm of theultra-high pressure mercury lamp by the UV reflection film 14, and cancondition the transmittance at the peak near 440 nm substantiallythrough the reflection by the blue conditioning film 14. Therefore, withthe UV cut filter 10 c, it is possible to prevent the deterioration ofcomponent parts by UV rays, to securely condition the excessively richblue color of the ultra-high pressure mercury lamp and thereby tocondition the color balance.

Incidentally, the UV cut filter 10 c according to the second embodimentalso does not substantially absorb UV rays and is therefore free of heatgeneration, so that it can be used also as a dustproof glass used in aliquid crystal display panel, as will be described later.

Next, a third embodiment of the UV cut filter according to the presentinvention will be described referring to FIGS. 13( a) and 13(b).

As shown in FIG. 13( a), the UV cut filter 10 d according to the thirdembodiment has a structure in which the above-mentioned blueconditioning film 15 is provided on one side of a UV absorptivelight-transmitting substrate 11 b, and an antireflection coating 13 isprovided on the other side.

The UV absorptive light-transmitting substrate 11 b is formed of a UVabsorptive glass, and has a performance insufficient for conditioningthe transmittance at the peak near 440 nm of the ultra-high pressuremercury lamp. Therefore, the blue conditioning film 15 has the functionof compensating for the performance of the UV absorptivelight-transmitting substrate 11 b, thereby conditioning thetransmittance at the peak near 440 nm of the ultra-high pressure mercurylamp.

The UV absorptive light-transmitting substrate 11 b has the function ofabsorbing UV rays and visible rays at wavelengths shorter than the peaknear 405 nm of the ultra-high pressure mercury lamp, for which it isnecessary that the half-power point is within a range of 415 to 430 nm.The transmittance characteristic of the blue conditioning film is thesame as above-described.

In Example 6 which will be described later, a UV cut filter 10 dcomprising a blue conditioning film 15 composed of a 9-layer film ofTiO₂—SiO₂ provided on one side of a UV absorptive glass 11 b of 1.1 mmin thickness and an antireflection coating 13 on the other side wasproduced. The absorption characteristic of the UV absorptive glass 11 bis indicated by the broken line {circle around (8)} in FIG. 13( b), andthe transmittance characteristic of the blue conditioning film 15 isindicated by the one-dotted chain line {circle around (3)} in FIG. 13(b). The spectral transmittance of the UV cut filter 10 d comprising thecombination of the UV absorptive glass and the blue conditioning film isindicated by the solid line {circle around (5)}. In the figure, the thinbroken line {circle around (7)} indicates the luminance characteristicof an ultra-high pressure mercury lamp.

The transmittance characteristic {circle around (8)} of the UVabsorptive glass is such that the peak near 405 nm can be cutsubstantially completely, but the transmittance variation is gradual andthe transmittance exceeds 90% in the vicinity of 440 nm, so that it isdifficult to cut the light at the peak near 440 nm by about 10 to 30%.

In the transmittance characteristic of the UV cut filter 10 d shown inFIG. 13( b), the influence of the transmittance of the blue conditioningfilm is heavy in the vicinity of 440 nm, and a step is observed there.The transmittance at 440 nm is about 75%.

The UV cut filter 10 d comprising the UV absorptive glass 11 b and theblue conditioning film 15 in combination as above can absorb UV rays andvisible rays at wavelengths shorter than the peak in 405 nm of theultra-high pressure mercury lamp by the UV absorptive glass 11 b, andcan condition the transmittance at the peak near 440 nm substantially bythe blue conditioning film 15. Therefore, with the UV cut filter 10 d,it is possible to prevent deterioration of component parts, to securelycondition the excessively rich blue color of the ultra-high pressuremercury lamp, and thereby to condition the color balance.

EXAMPLE 4

A UV cut filter 10 a comprising a stepped UV reflection film 12 providedon one side of a light-transmitting substrate 11 and an antireflectioncoating 13 provided on the other side of the light-transmittingsubstrate 11, as shown in FIG. 11( a), was produced.

Film formation was conducted by use of an RF ion plating apparatus (aproduct by SHOWA SHINKU CO., LTD.). An optical film thickness meter ofthe monochromatic optical monitor system was used. Correction plateslarger in width than usual were used, and the tooling coefficient wasset at 0.8. As the light-transmitting substrate 11, BK7 (a colorlessglass plate with n=1.52) was used. As the stepped UV reflection film 12,a 37-layer film filter comprising an alternate lamination of TiO₂—SiO₂was formed, the film constitution thereof being shown below, in which ahigh-refractive-index layer (TiO₂) is represented by H and alow-refractive-index layer (SiO₂) is represented by L.

The film constitution was 1L, 0.63H, 0.67L, 1.47H, 0.59L, (1.16H,0.83L)⁵, 1.08H, (0.91L, 1.03H)², 0.88L, (1.26H, 0.77L)⁵, 0.88H, 1.14L,1.04H, 0.67L, 1.04H, 1.9L, in this order from the substrate side (designwavelength: 370 nm). The spectral transmittance of the stepped UVreflection film 12 is indicated by the solid line {circle around (1)} inFIG. 11( c).

The stepped UV reflection film had a half-power point of 425 nm, and anaverage transmittance in a wavelength range of 428 to 450 nm (step) ofabout 85%. In a wavelength range of 460 to 520 nm, the transmittance wasas high as at least 97%.

In addition, as the antireflection coating, one having an ordinary4-layer constitution was formed. The film constitution was 0.23H, 0.4L,2.17H, 1L, in this order from the substrate side (design wavelength: 550nm).

EXAMPLE 5

A UV cut filter 10 c comprising a UV reflection film 14 on one side of alight-transmitting substrate 11 and a blue conditioning film 15 on theother side of the light-transmitting substrate 11, as shown in FIG. 12(a), was produced.

Film formation was conducted by use of an RF ion plating apparatus (aproduct by SHOWA SHINKU CO., LTD.). An optical film thickness meter ofthe monochromatic optical monitor system was used. Correction plateslarger in width than usual were used, and the tooling coefficient wasset at 0.8. As the light-transmitting substrate 11, BK7 was used. As theUV reflection film 14, a 33-layer film UV cut filter comprising analternate lamination of TiO₂—SiO₂ was formed, the film constitutionthereof being shown below.

The film constitution was 1L, 0.36H, 1.21L, 0.74H, 0.97L, 1.08H, 0.87L,1.08H, (0.88L, 1.15H)⁸, 0.88L, 1.12H, 0.9L, 1.01H, 1.02L, 1.03H, 0.71L,1.09H, 1.75L, in this order from the substrate side (design wavelength:365 nm). The half-power point was 425 nm. The spectral transmittance ofthis UV reflection film is indicated by {circle around (2)} in FIG. 12(b).

In addition, as the blue conditioning film 15, a 9-layer film ofTiO₂(H)—SiO₂(L) was formed, the film constitution thereof being shownbelow.

The film constitution was 1.22L, 0.25H, 0.57L, 2.68H, 0.31L, 2.42H,2.05L, 2.19H, 1.2L, in this order from the substrate side (designwavelength: 500 nm). The spectral transmittance of this blueconditioning film is indicated by {circle around (3)} in FIG. 12( b).

The blue conditioning film had a transmittance of 87.3% at 430 nm, atransmittance of 84.3% at 440 nm, a transmittance of 89.3% at 450 nm,and an average transmittance of 85.8% in a wavelength range of 430 to450 nm.

Besides, the spectral transmittance of the UV cut filter 10 c comprisingthe UV reflection film and the blue conditioning film in combination isindicated by the solid line {circle around (4)} in FIG. 12( b).

EXAMPLE 6

A UV cut filter 10 d comprising a UV absorptive glass 11 b of 1.1 mm inthickness as a light-transmitting substrate, the same blue conditioningfilm 15 as in Example 5 formed on one side of the UV absorptive glass 11b, and the same antireflection coating 13 as in Example 4 formed on theother side, as shown in FIG. 13( a), was produced.

The spectral transmittance of the UV absorptive glass is indicated bythe broken line {circle around (8)} in FIG. 13( b). Besides, thespectral transmittance of the blue conditioning film is indicated by theone-dotted chain line {circle around (3)} in the figure. The spectraltransmittance of the UV cut filter 10 d comprising the UV absorptiveglass and the blue conditioning film in combination is indicated by thesolid line {circle around (5)} in the figure.

Next, a dustproof glass for attaining the fifth object, a display panelfor attaining the sixth object, and a projection type display unit forattaining the seventh object will be described.

FIG. 14 shows a general constitution of a liquid crystal projector asone embodiment of the projection type display unit according to thepresent invention.

The liquid crystal projector 300 differs from the liquid crystalprojector 100 shown in FIG. 1 in that a display panel 20 according tothe present invention is used as the third liquid crystal panel formodulating blue color and, attendant on this arrangement, the UV cutfilter 10 is omitted. The other component parts are the same as in theliquid crystal projector 100 above, so that the same component parts asabove are denoted by the same symbols as above and the descriptionthereof is omitted.

In the conventional liquid crystal projector, on an optical path on theupstream side of a polarizing plate unit 131 disposed on the upstreamside of the third liquid crystal panel 20 for modulating blue color, aUV cut filter 10 has been disposed for protecting these component partsfrom UV rays.

In the liquid crystal projector 300 shown in FIG. 14, the display panelaccording to the present invention which is provided with a UVreflection film is used as the third liquid crystal display panel 20, sothat the UV cut filter 10 is unnecessary, the number of component partscan be reduced, compactness is enhanced, and cost is reduced.

FIG. 15 shows a sectional view of one embodiment of the third liquidcrystal display panel 20. The display panel 20 has a structure in whicha counter substrate 31 and a liquid crystal substrate 32 forconstituting a liquid crystal display unit 30 are spacedly disposed in atetragonal tubular case 21. The counter substrate 31 is disposed on theincidence side, and counter electrodes and an oriented film (not shown)are formed on the inside surface of the counter substrate 31 which isopposed to the liquid crystal substrate 32. The liquid crystal substrate32 is disposed on the emission side, and active devices such as TFTs andan oriented film (not shown) are formed on the inside surface of theliquid crystal substrate 32 which is opposed to the counter substrate31. A liquid crystal layer (not shown) is sealed between the countersubstrate 31 and the liquid crystal substrate 32. A flexible wiring 33connects the exterior of the case and the liquid crystal display unit 30to each other. A light-shielding film 34 called clearance is provided ina picture frame form on the outside surface of the counter substrate 31.An incidence side dustproof glass 41 is adhered to the incidence sidesurface of the counter substrate 31, and an emission side dustproofglass 42 is adhered to the emission side surface of the liquid crystalsubstrate 32.

The dustproof glasses 41 and 42 are for obviating the problem that whendust are deposited on the outside surfaces of the counter substrate 31and the liquid crystal substrate 32, the dust would be enlargedlyprojected onto the display. Specifically, the dustproof glasses 41 and42 have the function of spacing the dust from the liquid crystal displaysurface so as to achieve out-focusing, thereby making the deposition ofthe dust inconspicuous. Therefore, the dustproof glasses 41 and 42 havea large thickness of about 1.1 mm, and a glass such as quartz glass andNeoceram, the same material as the glass used in the liquid crystalsubstrate 32 and the counter substrate 31, is used therefor. Thedustproof glasses 41 and 42 are adhered respectively to the liquidcrystal substrate 32 and the counter substrate 31, in such a conditionas not to generate bubbles, with a transparent adhesive such as asilicone-based adhesive and an acrylic adhesive so conditioned as tohave a refractive index equal to that of the quartz glass or Neocerambeing used.

An antireflection coating has been provided on the outside surface ofthe incidence side dustproof glass 41 in the prior art. On the otherhand, in the present invention, a UV reflection film 50 is provided inplace of the antireflection coating. The UV reflection film 50 iscomposed of a dielectric multi-layer film. By appropriately selectingthe film design, it is possible to provide a steep characteristic suchthat light at wavelengths shorter than a specified wavelength is cutwhile light at longer wavelengths is transmitted. Thus, it is possibleto reflect UV rays and, if required, short-wavelength visible rays, andto enhance the transmittance for required visible rays.

As shown in FIG. 17, the transmittance characteristic of the UVreflection film is characterized in that the leading edge (about 425 nm)is steeper, UV rays (below 400 nm) are reflected substantiallycompletely, and the transmittance in the visible region (400 to 750 nm)on the longer wavelength side of the leading edge is higher, as comparedwith a UV absorptive glass. The transmittance for visible rays of atransparent glass substrate not provided with a UV reflection film isgenerally about 96%. Therefore, the UV reflection film functions as anantireflection coating in the visible region, and does not generateattenuation of the transmitted light; thus, the replacement of theconventional antireflection coating in the dustproof glass by the UVreflection film would not lead to a lowering in light quantity.

In addition, an antireflection coating 51 is provided on the outsidesurface of the emission side dustproof glass 42.

The first liquid crystal display panel 121 and the second liquid crystaldisplay panel 122 used in the above-mentioned liquid crystal projector300 have a structure in which the UV reflection film 50 of the displaypanel 10 according to the present invention is replaced with anantireflection coating, and have no other special difference instructure.

Incidentally, the dustproof glasses 41 and 42 may not be adhered to butbe spaced from the counter substrate 31 and the liquid crystal substrate32, respectively. Where the dustproof glasses 41 and 42 are spacedlydisposed, air layers are intermediately present between the dustproofglasses 41 and 42 and the counter substrate 31 and the liquid crystalsubstrate 32, and reflection of light is thereby generated; in view ofthis, antireflection coatings are provided on the inner sides of thedustproof glasses 41 and 42 and on the outer sides of the countersubstrate 31 and the liquid crystal substrate 32.

The display panel 20 according to the present invention comprises thedustproof glass 41 provided with the UV reflection film 50 on theincidence side, so that it can reflect UV rays and, if required,short-wavelength visible rays by the UV reflection film 50, whereby onlythe required visible rays can be incident on the liquid crystal displayunit 30. Therefore, the liquid crystal display unit 30 can be protectedfrom UV rays, deterioration of the oriented film and other organicmatters by UV rays can be prevented, and reliability can be enhanced. Inaddition, the liquid crystal display unit 30 and the dustproof glass 41can be prevented from being heated to a high temperature throughabsorption of UV rays, and generation of non-uniformity or the like inthe projected image is obviated.

FIGS. 16( a) and 16(b) show sectional structures of embodiments of thedustproof glass according to the present invention. FIG. 16( a) shows adustproof glass of the type of being adhered to the liquid crystaldisplay unit, and FIG. 16( b) shows a dustproof glass of the type ofbeing spaced from the liquid crystal display unit.

The dustproof glass 41 shown in FIG. 16( a) has a structure in which aUV reflection film 50 is provided on one side of a transparent glasssubstrate 40, and no film is provided on the other side. The transparentglass substrate 40 is formed of a glass which is the same material asthe counter substrate 31. Examples of the glass include quartz glass,Neoceram, 7971 titanium silicate glass (a product by Corning), sapphireglass, etc. The thickness of the transparent glass substrate 40 is about0.7 to 3 mm, such a value that dust can be spaced sufficiently from theincidence surface of the counter substrate 31 and can thereby be set outof focus. Too large a thickness leads to the problems of a lowering ofheat radiation property and an increase in weight.

As shown in FIG. 15, the dustproof glass 41 is used as a part of thedisplay panel 20 in such a manner that its surface not provided thereonwith a film is adhered, with an adhesive, to the incidence sidesubstrate surface of the liquid crystal display unit 30 on which theUV-containing light from the light source is incident.

The dustproof glass 43 shown in FIG. 16( b) has a structure in which aUV reflection film 50 is provided on one side of a transparent glasssubstrate 40, and an antireflection coating 51 is provided on the otherside. The dustproof glass 43 is spaced from the incidence side substratesurface of the liquid crystal display unit 30 on which the UV-containinglight from the light source is incident, with its UV reflection film 50on the outside and with its antireflection coating 51 on the inside, andis used as a part of the liquid crystal display panel. The transparentglass substrate 40 of the dustproof glass 43 may be made of a materialdifferent from that of the counter substrate 31, and, generally, aninorganic glass is used as the material. Examples of the materialinclude soda lime glass, borosilicate glass, lead glass, alkali-freeglass, quartz glass, Neoceram, 7971 titanium silicate glass (a productby Corning), sapphire glass, etc.

As the UV reflection film 50, there may be used a UV reflection filmused in a UV cut filter which can reflect UV rays having wavelengthsshorter than 400 nm. In a projection type display unit using anultra-high pressure mercury lamp as a light source, it is preferable toset a half-power point in a range of 425 to 440 nm, particularly in thevicinity of 430 to 435 nm, so that the peak near 440 nm of theultra-high pressure mercury lamp can be partly reflected by 10 to 30%,preferably about 10 to 20%. As such a UV reflection film, there can beused the multi-layer film cut filter according to the present inventionin which the ratio H/L or L/H indicating the balance in optical filmthickness between a high-refractive-index layer H and alow-refractive-index layer L in the repeated alternate layer is setwithin a range of 1.2 to 2.0.

In addition, as a particularly preferable UV reflection film in the casewhere the light source 101 is an ultra-high pressure mercury lamp, theabove-mentioned stepped UV reflection film 14 can be used preferably.Therefore, as the dustproof glass 41 according to the present inventionof the type of being adhered to the liquid crystal display unit 30,there can be preferably adopted the UV cut filter 10 b having astructure as shown in FIG. 11( b) in which the stepped UV reflectionfilm 12 is provided on one side of the light-transmitting substrate 11,and no film is provided on the other side of the light-transmittingsubstrate 11. Besides, as the dustproof glass 43 of the type of beingspaced from the liquid crystal display unit 30, there can be preferablyadopted the UV cut filter 10 a having a structure as shown in FIG. 11(a) in which the stepped UV reflection film 12 is provided on one side ofthe light-transmitting substrate 11, and the antireflection coating 13is provided on the other side of the light-transmitting substrate 11.

Furthermore, as the dustproof glass of the type of being spaced from theliquid crystal display unit 30, there can be preferably adopted the UVcut filter 10 c having a structure as shown in FIG. 12( a) in which theUV reflection film 14 is provided on one side of the light-transmittingsubstrate 11, and the blue conditioning film 15 as a reflective film forblue color is provided on the other side of the light-transmittingsubstrate 11.

As has been described above, the multi-layer film cut filter accordingto the present invention differs from the conventional one in filmthickness balance of the repeated alternate layer, whereby control offilm thickness is facilitated, and the multi-layer film can be formedwith high accuracy, resulting in that the multi-layer film cut filterhas characteristics as designed.

According to the method of producing a multi-layer cut filter accordingto the present invention, the tooling coefficient is set low so that athicker layer is formed on the monitor substrate, whereby control offilm thickness is facilitated, and a multi-layer film cut filter havingcharacteristics as designed can be produced.

The UV cut filter according to the present invention uses the stepped UVreflection film, whereby the UV cut filter is provided withtransmittance characteristic adjusted to the luminance characteristic ofan ultra-high pressure mercury lamp, deterioration of component parts byUV rays can be prevented, the excessively rich blue color of theultra-high pressure mercury lamp can be securely reduced, and colorbalance can thereby be conditioned.

In addition, the UV cut filter according to the present inventioncomprises the UV reflection film and the blue conditioning film incombination, whereby the UV cut filter is provided with transmittancecharacteristic adjusted to the luminance characteristic of an ultra-highpressure mercury lamp, deterioration of component parts by UV rays canbe prevented, the excessively rich blue color can be securely reduced,and color balance can thereby be conditioned.

The UV cut filter according to the present invention comprises the UVabsorptive glass and the blue conditioning film in combination, wherebythe UV cut filter is provided with transmittance characteristic adjustedto the luminance characteristic of an ultra-high pressure mercury lamp,deterioration of component parts by UV rays can be prevented, theexcessively rich blue color of the ultra-high pressure mercury lamp canbe securely reduced, and color balance can thereby be conditioned.

The projection type display unit according to the present invention usesthe UV cut filter having transmittance characteristic adjusted to theluminance characteristic of an ultra-high pressure mercury lamp, wherebydeterioration of component parts by UV rays can be prevented, and theexcessively rich blue color of the ultra-high pressure mercury lamp canbe securely reduced, to obtain a good color balance.

The dustproof glass according to the present invention is provided withthe UV reflection film in place of the antireflection coating, wherebythe dustproof glass is provided with such a characteristic as to reflectharmful UV rays and the like without lowering the transmittance foruseful visible rays.

The display panel according to the present invention has a structure inwhich the dustproof glass provided thereon with the UV reflection filmis incorporated therein, whereby the display unit can be protected fromUV rays without using a UV cut filter as a component part.

The projection type display unit according to the present invention usesthe display panel in which the dustproof glass provided thereon with theUV reflection film is incorporated, whereby a UV cut filter as acomponent part is unnecessitated, and the number of component parts canthereby be reduced.

INDUSTRIAL APPLICABILITY

The filter according to the present invention is used, for example, in aprojection type display unit, and can be applied to the use for cuttingharmful UV rays and short-wavelength visible rays from UV-containinglight emitted from a light source, thereby preventing deterioration ofcomponent parts by UV rays and the like.

The method of producing a multi-layer film cut filter according to thepresent invention makes it possible to produce a filter used for thepurpose of cutting harmful UV rays and short-wavelength visible raysfrom UV-containing light emitted from a light source, thereby preventingdeterioration of component parts by UV rays and the like.

The dustproof glass according to the present invention is incorporated,for example, in a liquid crystal display panel of a projection typedisplay unit, and can be applied to the use for cutting harmful UV raysand short-wavelength visible rays from UV-containing light emitted froma light source, thereby preventing deterioration of the display panel byUV rays and the like.

The projection type display unit according to the present invention canbe applied to the use for enlarged projection of images onto a screen.

1. A multi-layer film cut filter comprising a dielectric multi-layerfilm formed on a light-transmitting substrate, said dielectricmulti-layer film comprising a repeated alternate layer composed of arepeated alternate lamination of a high-refractive-index layer and alow-refractive-index layer in an equal optical film thickness, whereinthe ratio H/L or L/H in said repeated alternate layer is within a rangeof 1.2 to 2.0, where H is the optical film thickness of saidhigh-refractive-index layer and L is the optical film thickness of saidlow-refractive-index layer.
 2. A method of producing a multi-layer filmcut filter, comprising the steps of repeatedly building up particlesflying from a vapor source for forming high-refractive-index layers andparticles flying from a vapor source for forming low-refractive-indexlayers on a light-transmitting substrate, simultaneously building uplayers also on a monitor substrate, and conducting film thicknesscontrol while measuring the optical film thickness of said layer formedon said monitor substrate, wherein a correction plate is interposedbetween said vapor source and said light-transmitting substrate, and atooling coefficient, which is the ratio of the film thickness of saidlayer deposited on said light-transmitting substrate to the filmthickness of said layer deposited on said monitor substrate, is setwithin a range of 0.6 to 0.85.
 3. A method of producing a multi-layerfilm cut filter as set forth in claim 2, wherein a repeated alternatelayer composed of a repeated alternate lamination of saidhigh-refractive-index layer and said low-refractive-index layer inrespectively equal optical film thicknesses is formed, and the ratio H/Lor L/H in said repeated alternate layer is within a range of 1.2 to 2.0,where H is the optical film thickness of said high-refractive-indexlayer and L is the optical film thickness of said low-refractive-indexlayer.
 4. A UV cut filter wherein a stepped UV reflection film having ahalf-power point of 415 to 430 nm, an average transmittance of 70 to 90%in a wavelength range of 430 to 450 nm, and a transmittance of at least90% in a wavelength range of 460 to 520 nm is provided on one side of alight-transmitting substrate.
 5. A UV cut filter as set forth in claim4, wherein said stepped UV reflection film is comprised of a dielectricmulti-layer film, which comprises a repeated alternate layer composed ofa repeated alternate lamination of a high-refractive-index layer and alow-refractive-index layer in respectively equal optical filmthicknesses, and the ratio H/L or L/H in said repeated alternate layeris within a range of 1.2 to 2.0, where H is the optical film thicknessof said high-refractive-index layer and L is the optical film thicknessof said low-refractive-index layer.
 6. A UV cut filter wherein a UVreflection film having a half-power point of 415 to 430 nm is providedon one side of a light-transmitting substrate, and a blue conditioningfilm having an average transmittance of 70 to 90% in a wavelength rangeof 430 to 450 nm and a transmittance of at least 90% in a wavelengthrange of 460 to 520 nm is provided on the other side of saidlight-transmitting substrate.
 7. A UV cut filter as set forth in claim6, wherein said UV reflection film is comprised of a dielectricmulti-layer film, which comprises a repeated alternate layer composed ofa repeated alternate lamination of a high-refractive-index layer and alow-refractive-index layer in respectively equal optical filmthicknesses, and the ratio H/L or L/H in said repeated alternate layeris within a range of 1.2 to 2.0, where H is the optical film thicknessof said high-refractive-index layer and L is the optical film thicknessof said low-refractive-index layer.
 8. A UV cut filter wherein a blueconditioning film having an average transmittance of 70 to 90% in awavelength range of 430 to 450 nm and a transmittance of at least 90% ina wavelength range of 460 to 520 nm is provided on one side of a UVabsorptive light-transmitting substrate having an absorptivecharacteristic with a half-power point of 415 to 430 nm.
 9. A projectiontype display unit comprising a light source constituted of an ultra-highpressure mercury lamp, a display panel for forming a predetermined imageby modulating light from said light source, a UV cut filter disposed onan optical path between said light source and said display panel, and anenlarged-projection optical system for enlarged projection of lightemitted from said display panel, wherein said UV cut filter comprises astepped UV reflection film provided on one side of a light-transmittingsubstrate, said stepped UV reflection film having a half-power point of415 to 430 nm, an average transmittance of 70 to 90% in a wavelengthrange of 430 to 450 nm, and a transmittance of at least 90% in awavelength range of 460 to 520 nm.
 10. A projection type display unitcomprising a light source constituted of an ultra-high pressure mercurylamp, a display panel for forming a predetermined image by modulatinglight from said light source, a UV cut filter disposed on an opticalpath between said light source and said display panel, and anenlarged-projection optical system for enlarged projection of lightemitted from said display panel, wherein said UV cut filter has astructure in which a UV reflection film having a half-power point of 415to 430 nm is provided on one side of a light-transmitting substrate, anda blue conditioning film having an average transmittance of 70 to 90% ina wavelength range of 430 to 450 nm and a transmittance of at least 90%in a wavelength range of 460 to 520 nm is provided on the other side ofsaid light-transmitting substrate.
 11. A projection type display unitcomprising a light source constituted of an ultra-high pressure mercurylamp, a display panel for forming a predetermined image by modulatinglight from said light source, a UV cut filter disposed on an opticalpath between said light source and said display panel, and anenlarged-projection optical system for enlarged projection of lightemitted from said display panel, wherein said UV cut filter has astructure in which a blue conditioning film having an averagetransmittance of 70 to 90% in a wavelength range of 430 to 450 nm and atransmittance of at least 90% in a wavelength range of 460 to 520 nm isprovided on one side of a UV absorptive light-transmitting substratehaving an absorption characteristic with a half-power point of 415 to430 nm.
 12. A dustproof glass for preventing deposition of dust on adisplay unit for forming a predetermined image by modulating light froma light source, said dustproof glass disposed on the upstream side ofsaid display unit on which said light from said light source is incidenton said display unit, wherein a UV reflection film is provided on oneside of a transparent glass substrate and, said UV reflection film iscomprised of a dielectric multi-layer film, which comprises a repeatedalternate layer composed of a repeated alternate lamination of ahigh-refractive-index layer and a low-refractive-index layer inrespectively equal film thicknesses, and the ratio H/L or L/H in saidrepeated alternate layer is in the range of 1.2 to 2.0, where H is theoptical film thickness of said high-refractive-index layer and L is theoptical film thickness of said low-refractive-index layer.
 13. Adustproof glass as set forth in claim 12, wherein said UV reflectionfilm is a stepped UV reflection film having a half-power point of 415 to430 nm, an average transmittance of 70 to 90% in a wavelength range of430 to 450 nm, and a transmittance of at least 90% in a wavelength rangeof 460 to 520 nm.
 14. A dustproof glass as set forth in claim 12,wherein a UV reflection film having a half-power point of 415 to 430 nmis provided on one side of said transparent glass substrate, and a blueconditioning film having an average transmittance of 70 to 90% in awavelength range of 430 to 450 nm and a transmittance of at least 90% ina wavelength range of 460 to 520 nm is provided on the other side ofsaid transparent glass substrate.
 15. A display panel comprising adisplay unit for forming a predetermined image by modulating light froma light source, and a dustproof glass for preventing deposition of duston said display unit, said dustproof glass disposed on the upstream sideof said display unit on which said light from said light source isincident on said display unit, wherein said dustproof glass comprises aUV reflection film on the upstream side of a transparent glasssubstrate, and said UV reflection film is comprised of a dielectricmulti-layer film, which comprises a repeated alternate layer composed ofa repeated alternate lamination of a high-refractive-index layer and alow-refractive-index layer in respectively equal film thicknesses, andthe ratio H/L or L/H in said repeated alternate layer is in the range of1.2 to 2.0, where H is the optical film thickness of saidhigh-refractive-index layer and L is the optical film thickness of saidlow-refractive-index layer.
 16. A display panel as set forth in claim15, wherein said UV reflection film is a stepped UV reflection filmhaving a half-power point of 415 to 430 nm, an average transmittance of70 to 90% in a wavelength range of 430 to 450 nm, and a transmittance ofat least 90% in a wavelength range of 460 to 520 nm.
 17. A display panelas set forth in claim 15, wherein said dustproof glass has a structurein which a UV reflection film having a half-power point of 415 to 430 nmis provided on one side of said transparent glass substrate, and a blueconditioning film having an average transmittance of 70 to 90% in awavelength range of 430 to 450 nm and a transmittance of at least 90% ina wavelength range of 460 to 520 nm is provided on the other side ofsaid transparent glass substrate.
 18. A projection type display unitcomprising: a light source; a display panel comprising a display unitfor forming a predetermined image by modulating light from said lightsource, and a dustproof glass for preventing deposition of dust on saiddisplay unit, said dustproof glass disposed on the upstream side of saiddisplay unit on which said light from said light source is incident onsaid display unit; and an enlarged-projection optical system forenlarged projection of light emitted from said display panel, whereinsaid dustproof glass comprises a UV reflection film on the upstream sideof a transparent glass substrate, and said UV reflection film iscomprised of a dielectric multi-layer film, which comprises a repeatedalternate layer composed of a repeated alternate lamination of ahigh-refractive-index layer and a low-refractive-index layer inrespectively equal optical film thicknesses, and the ratio H/L or L/H insaid repeated alternate layer is in the range of 1.2 to 2.0, where H isthe optical film thickness of said high-refractive-index layer and L isthe optical film thickness of said low-refractive-index layer.
 19. Aprojection type display unit as set forth in claim 18, wherein said UVreflection film is a stepped UV reflection film having a half-powerpoint of 415 to 430 nm, an average transmittance of 70 to 90% in awavelength range of 430 to 450 nm, and a transmittance of at least 90%in a wavelength range of 460 to 520 nm.
 20. A projection type displayunit as set forth in claim 18, wherein said dustproof glass has astructure in which a UV reflection film having a half-power point of 415to 430 nm is provided on one side of said transparent glass substrate,and a blue conditioning film having an average transmittance of 70 to90% in a wavelength range of 430 to 450 nm and a transmittance of atleast 90% in a wavelength range of 460 to 520 nm is provided on theother side of said transparent glass substrate.